Solar Energy Conversion and Catalysis Calculations
First principles calculations of molecules and materials will be conducted with a focus on advanced solar energy conversion processes, including dye-sensitized solar cells, artificial photosynthesis, and organic solar cells. The complexity of these systems, both in terms in molecular structure (supramolecular and nanostructured materials) and function (photoinduced processes involving excited states), makes it vital to use high-performance computing facilities for accurate computational studies. The ambition here is firstly to provide a better understanding of how solar energy conversion systems function on the molecular level, and secondly to use calculations to guide the search for more efficient molecular components in such systems. We mainly use Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) calculations, complemented with e.g. Reactive Force Field methods (ReaxFF). A. Excited States of Light-harvesting molecules Excited states of organic molecules, transition metal complexes, and polymers used for solar energy conversion applications will be studied quantum chemically using first principles (time-dependent DFT and multi-reference ab initio) methods. A1. Photoexcitation: Tuning the absorption spectrum for improved absorption through computational screening of electron donating and withdrawing substituents. A2. Excited State Potential Energy Surfaces (PESs): Investigating PESs of low-lying excited singlet and triplet states of dye molecules and natural pigements to predict the structure of excited state deactivation pathways and charge-separation. B. Structural and Electronic Properties of Dye-Sensitized Nanocrystals The structure and stability of metal oxide nanocrystals, e.g. TiO2, will be investigated using a combination of quantum chemical structure optimizations and molecular dynamics simulations on realistic atomistic models in the 1 - 10 nm size range. Electronic properties, such as band gaps, will be calculated e.g. at the DFT and TD-DFT levels of theory.Current interests also include III-V semiconducting nanocrystalline materials. B1. Structural stability of dye-nanocrystal interfaces: Study binding strengths of anchor groups, binding ligands, and dyes to metal oxide substrates. Investigate bi- and tri-podal anchors with large footprints from Galoppini. B2. Interfacial electronic structure: Investigate how to improve the energy matching of the ground and excited states of dyes to the substrate band structure in DSSCs for improved current-voltage characteristics. Suitable molecules e.g. organic polycyclic aromatic molecules and Ru-bistridenate complexes have been selected for accurate calculations. B3. Surface electron transfer: Predict heterogeneous electron transfer (ET) rates from calculated interfacial electronic coupling strengths. Elucidate how the ET rate is influenced by various anchor and spacer groups. Focus on weak electronic coupling through rigid rod spacer groups including new so called "Ru-star" Complexes. This requires use of larger cluster models, say (TiO2)n with n>100. C. Heterogeneous interfaces and catalysis A multi-scale combination of quantum chemical calculations and molecular dynamics simulations, e.g. using reactive force fields will be applied to studies of molecular functionalization of metal oxide substrates and heterogeneous catalysis on metal oxide substrates including, in particular, TiO2. This project continues and expands previous SNIC project on neolith (SNIC 001/11-147), and platon (SNIC 001/11-131).